Air separation method for slurry separation



"A, B. ANDERSEN Erm. l

Filed June' 14. 1944 AIRSEPARATIONHETHOD FOR SLURRY SEPARATION Tln Feb.15', 1949.

Patented Feb. 15, 1949 AIR SEPARATION METHOD FOR SLURRY SEPARATION AxelBrix Andersen, Larchmont, and Knud Horn, New York, N. Y., assignors toF. L. Smidth & Co., New York. N. Y.. a corporation of New JerseyApplication June i4, 1944, Serial No. 540,284 s claims. (ci. 2oz-139)This invention relates to the treatment of material in slurry form forthe purpose of separatpreparation of the raw materials to be burned.

into clinker, the mining industry, etc. For purposes of explanation, theuse of the new method in the treatment of cement raw material slurrywill be illustrated and described in detail, but it will be evident thatthe utility of the invention is not limited to the treatment of a slurryof that particular kind.

In closed circuit grinding as practiced in the cement and miningindustries, it is essential that all particles ground to the requiredneness be removed from the slurry circulated through the mill. Also, ina cement raw material slurry of normal neness, the size of theindividual grains varies from 90 microns to less than 1 micron and theseparation of the material into fractions containing particles ofdifferent size is necessary or desirable for various reasons. Someslurries contain substantial quantities of slimes and the removal-ofsuch slimes may be desirable in order to facilitate other steps in theseparation y process or because the slimes contain impuri- Vties whichshould be removed.

At the present time, apparatus of various kinds,

such as centrifuges, bowl classifiers, and hydroseparators, are used inthe separation of slurries into fractions containing particles ofdifferent size, but such apparatus is frequently large and expensive andthe use of certain types of such apparatus requires dilution of' theslurry with large amounts of Water. After treatment in such apparatus,the excess water should be removed from the fractions, which areultimately to be burned, in order that fuel may be conserved, but itisoften difficult to carry on such dewatering with the result that thematerial contains an amount of water in excess of that required to makeit pumpable.

In some instances, the slurry contains particles of the same weight andsize but of different composition and, in that event, flotation may beemployed to separate the particles of different composition. In order tofacilitate flotation, the slurry is usually' deslimed in a preliminaryoperation, although, in some instances, flotation of slime material hasbeen practiced. It is not certain, however, that the flotation of slimesis of general application. Flotation processes depend on the use ofreagents which coat the particles selectively and, to obtain the bestresults, the reagent used must be well mixed with the slurry, theflotation time should be as short as possible vin order that the reagentwill not coat both the concentrate and the reject particles, and thecolloidal effect of extremely fine particles should be eliminated, forexample, by the addition of a dispersing agent. As these requirementsare contradictory, they cannot all be fullled on conventional flotationmachines and the process is, therefore, somewhat ineicient.

The present invention is directed to the provision of a novel method, bywhich slurry may be treated tol produce fractions containing particlesof different size without excessive dilution of the slurry or the use oflarge and expensive apparatus. The method depends for its functioning onthe breaking up or atomization of the slurry into drops of fine size,which may be particles with a thin coating of moisture thereon or, insome instances, entirely of water. The slurry is atomized into a currentof air. and the drops are suspended in the air for a longer or shortertime, depending on rtheir size and -specic gravity. The drops thus .fallout of the current of air at different' places and fractions of theslurry containing particles of-different size can, accordingly, becollected at different points along the path of flow of the current.

The method may be conveniently practiced by creating a current of airthrough an enclosed space and discharging the slurry into or across theair current by atomizing the slurry by means of air under pres-sure orby mechanical means only. The fractions of the slurry are then collectedat the boundary of the space at pointsv at different distances from theplace where the atomization occurs. A convenient form of apparatus forthe purpose includes a vertical chamber into which air under pressure isintroduced near the lower end to ow upwardly and escape at the top. Theslurry is atomized by a suitable nozzle mounted within the chamberbetween the ends thereof and the spray so formed is dischargedsubstantially horizontally across the path of the upwardly flowingcurrent. The air steam suspends the lighter particles so that theytravel upwardly and outwardly toward the wall of the chamber and may becollected along the chamber wall at a level abovev that of the atomizingnozzle, while the heavier particles fall through :Masse the air streamand are collected along the wall of the chamber at lower levels. In theuse of such apparatus, the air may be introduced under pressure tocreate a stream oi such velocity that the lightest drops, which willinclude drops of water and slimes, will be carried out of the chamber,so that desliming and dewatering will be effected.

In the treatment of a slurry which contains particles to be separated,which are of the same size and specific gravity but of differentmaterials, the slurry may be mixed with flotation reagents which Willselectively coat the particles -of the diilerent materials, the reagentsused being collecting and frothing agents commonly employed in flotationpractice and well known to the art. The mixing is preferably effectedimmediately ahead of the atomizing nozzle, by which the mixture isatomized and the individual particles set free. The reagents adhere tothe particles of one type only so that, in the atomization, the coatedparticles acquire a surrounding air bubble which lowers their specificgravity and results in their suspension in the air stream for a longertime than the particles not coated by the reagents. Because of thisdifference in the specific gravities of the coated and uncoatedparticles, they can be separated according to the method in the same Wayas uncoated particles of different specific gravities.

For a better understanding of the invention, reference may be had to theaccompanying drawing, in which Fig. 1 is a View in vertical section ofapparatus which may be used in the practice of the new process;

Fig. 2 is a sectional view of a modified type of nozzle; and

Fig. 3 is a bottom plan view of the nozzle shown in Fig. 2.

The apparatus illustrated includes a vertical chamber I which may bemade of any suitable material, such as sheet metal, and is provided witha conical top II from which leads an outlet conduit I2. A baille I3 ismounted within the top in front of the discharge opening to interceptthe outowing air and create turbulence which will permit particlescarried by the air stream to drop out of the stream.

An atomizing nozzle I4 is mounted within the chamber in any suitablemanner, as on cross arms I5, and the nozzle may be of conventional typeand atomize either by mechanical means only or by means of compressedair. The nozzle illustrated is of the latter type and it is suppliedwith slurry through a line I 6 leading from a pump I1, which receivesslurry from a tank I8 at any convenient location. Compressed air foreffecting atomization of the slurry is supplied to the nozzle through aline I9 and the nozzle is provided with a multiplicity of dischargeopenings and discharges the slurry outwardly substan tiallyhorizontally, as, for example, in the form of a fiat cone.

The nozzle is mounted on a shank 20 in a supporting member 2| on thearms I5 and may be raised or lowered, as may be desired. The pipes I6and I9 extendoutward from the nozzle through an opening 22 in the wallof the chamber and pass through a plate 23 which closes the opening andmay be adjusted up or down as the nozzle is raised or lowered.

At its lower end, the chamber Ill is formed with a hopper-like bottom 24through the wall of which extends an air inlet conduit 25 leading to 4 amain discharge head 26 provided with a number of nozzles 2l, 28. Thenozzles 21 direct air streams in a generally upward and tangentialdirection. while nozzles 28 direct the air upwardly. The air conduit isconnected to the discharge outlet ci a ian 26a, theintake of which isconnected to the conduit I2, so that the air withdrawn from the chambermay be recirculated. The conduit I2 is provided near its lower end witha collecting trap 29 having a valved outlet 30 through which slurry,which has been carried out of the chamberinto the conduit, may becollected and withdrawn.

The bottom 24 of the chamber is provided with a slurry discharge pipe 3lwhich may lead into a sump 32 so that the end of the pipe lies beneaththe level of the slurry in the sump. A quantity of slurry is thuscontinuously maintained in the pipe and air is prevented from escapingfrom the chamber through the pipe.

- A circumferential trough 33 is mounted on the inner wall of thechamber with its upper edge somewhat above the level of the nozzle I4and this trough has a draw-oil pipe 34 which may lead into a sumpsimilar to sump 32. Within the trough is a tubular partition member 35mounted on rods 3G extending outward through openings in the wall ofchamber I0. The rods pass through slots in the vertical wall of thetrough and the arrangement is such that the tubular partition member 35may be placed in different positions of adjustment with its top edge atdifferent levels above the upper edge of the trough. The partition 35flares outwardly at its lower end, as indicated at 31.

Below a trough 33 is a similar trough 38 haveA ing a discharge pipe 39leading into a sump, and a tubular partition 40, which is similar topartition 35, is mounted within trough 38 on rods 40 4I. The ared loweredge 31 of the partition 35 extends outwardly so as to lie above trough38 and the partition 4B is flared at its lower end 40 so that its edgelies outward beyond nozzles 21 on head 2B.

The nozzle shown in Fig. 2 includes a block 42 having a central chamber43 into which slurry is introduced through a pipe 44, the lower end ofthe chamber 43 being conical and closed by a threaded member 45 providedwith a discharge opening 36. Compressed air is supplied to the nozzle bya pipe 41 and enters a passage 4B leading to an annular chamber 9. Fromthis chamber lead a plurality of discharge passages 53 formed in member55. The member 45 has a generally conical recess 5I in its lower faceand the passages 50 open through the face of that recess. The passagesextend generally tangentially and direct air streams against the slurryissuing from the discharge opening 46 and cause the slurry to be brokenup into minute drops which form a flat cone.

In the practice of the new method by the apparatus disclosecha currentof air is maintained through the chamber lil by fan 26a and the slurryis atomized in the nozzle I4. The minute drops forming the mist or sprayof slurry then move outwardly from the nozzle across the upwardly movingcurrent of air. The drops containing the lightest particles pass to thewall of the chamber in the region above the trough 33 and are collectedin that trough and carried away through the discharge pipe 34. Theheavier particles fall through the current of air to be collected eitherin the lower trough 38 or in the bottom of the chamber. By regulatingthe velocity of the air stream, some of the lightest droplets, includingthose made up entirely of water or containing the slimes, may b ecarried out of the chamber, so that the slurry being treated may beeither dewatered or deslimed or both.

The separation at different particle sizes can be controlled by varyingthe vertical position of the nozzle with relation to the troughs 33 and38 and also by adjusting the position of tubular partitions 35, 40 withrelation to the troughs in which they are mounted. When partition 35 israised, its upper edge tends to intercept a certain number of thedroplets which would otherwise enter trough 33, and the materialimpinging on theinner surface of partition 35 runs down the partitionand then drips olf the flared lower edge thereof into trough 38. Similarlowering of partition 35 permits droplets, which would otherwise beintercepted by the partition, to enter trough 33.

In the practice of the new method, it has been found that a goodseparation may be obtained and the materials collected in the differenttroughsshow on analysis that the fraction in trough 33 contains aconsiderably greater proportion of fine particles than the fractionscollected in the lower'trough and at the bottom of the chamber. It hasalso been found that in the treatment of slurries having a comparativelyhigh water content, the fraction in trough 33 will contain considerablymore water than the fraction in the lower trough.

When flotation reagents are to be employed, they will be introduced intothe slurry line l0 leading to nozzle Il or into the intake of pump l1.In either case, a thorough mixing of the reagents and the slurry isobtained and the reagents are in contact with the particles for so shorta time that selective coating of the par'- ticles is obtained. l

As mentioned above, a mechanical atomizer may be used for dischargingthe slurry, instead of the compressed air atomizer shown. Such amechanical atomizer may be of the usual type which includes a rapidlyrotating disc or impeller by'means of which the slurry is discharged bycentrifugal action.

By the term slurry, as used in the appended claims, we refer to amixture of small solid particles of a size not to exceed about 90microns, and liquid. Such a slurry varies in viscosity, depending uponits liquid content, but, as ordinariiyproduced and used in the cementindustry, for example, it is quite thick. In a slurry, the particles arebound together bythe surface tension of the liquid and the materialbehaves like s'. homogeneous fluid. l

We claim:

1. A method of treating slurry. which comprises creating a current ofair through anenclosed space. discharging slurry into the air current byatomizing the slurry to form a fine spray thereof, the air currentcausing the drops of slurry to be carried along with it for distancesvarying inversely with the specific gravity of the drops, and separatelycollecting fractions of the slurry at points spaced along the path offlow of the air.

2. A method of treating slurry which comprises creating a current of airthrough an enclosed space, discharging slurry into the air current intoa fine spray,

slurry at points along the boundary of the space across the direction offlow of the current by atomlzing the slurry to form a fine spraythereof, the air current causing the drops of slurry to be carried alongwith it for distances varying inversely with the specific gravity' ofthe drops, and separately collecting fractions of the slurry at pointsspaced along thepath of flow of the air.

3. A method of treating slurry which comprises creating an upwardcurrent of air through an enclosed space, discharging slurry byatomizing it into the air current across the direction of flow of thecurrent, the atomizationforming the slurry into a line spray and the aircurrent causing the drops of slurry to be carried along with it fordistances varying-inversely with the specific gravity of the drops, andseparately collecting fractions of the slurry at points spaced along thepath of flow of the air, part of the fractions being collected above thelevel at which the atomized slurry enters the air current.

4. A method of treating slurry which comprises creating an upwardcurrent of air through an enclosed space, discharging slurry byatomizing it into the air current across the direction of now of thecurrent, the atomization forming the slurry into a fine spray, andcollecting fractions of the slurry at points spaced along the path ofnow of the air, part of said fractions being collected below and partabove the level at which the atomized slurry enters the air current.

- 5. A method of treating slurry which comprises creating .an upwardcurrent of air through an enclosed space, discharging slurry byatomizlng it into the air current across the direction of now of thecurrent, the atomization forming the slurry and collecting fractions ofthe above and below the level at which the atomixed slurry enters theairl current. g

6. A method of treating slurry which comprises creating a current of airthrough an enclosedA space, discharging slurry into the air current byatomizing the slurry, to form a fine spray thereof, the current being ofsuch velocity as to carry the drops of slurry varying inversely with thespecific gravity of the dropsand to carry a fraction of the slurry outof the space, and separately collecting the slurry not carried out ofthe space in fractions at points spaced along the pathof flow of theair.

AXEL BRIX ANDERSEN. KNUD HORN.

REFERENCES CITED The following references are of record in the nie ofthis patent:

UNITED sTa'ms PATENTS France June 26, 1938 along with `it for distances

